Abstract
ABA triblock polyesters are synthesized using a commercially available chromium salen catalyst, in one pot, from monomer mixtures comprising epoxide, anhydride and lactone. The catalysis is highly selective and applies a single catalyst in two distinct pathways. It occurs first by epoxide/anhydride ring‐opening copolymerization and subsequently by lactone ring‐opening polymerization. It is used to produce various new ABA polyester polyols; these polyols can undergo post‐functionalization and chain‐extension reactions. The ability to use a commercial catalyst and switchable catalysis with monomer mixtures is expected to facilitate future explorations of new classes of block polymers.
Highlights
ABA triblock polyesters are synthesized using a commercially available chromium salen catalyst, in one pot, from monomer mixtures comprising epoxide, anhydride and lactone
Block polyesters are synthesized by sequential polymerization reactions and/or with macro-initiators—such methods can be limited by the conversion efficiency, intermediary purification steps, and by the nature of the repeat unit chemistry
Understanding the reaction was hindered as the sole lactone investigated was bbutyrolactone, which can ring-open at two sites complicating enchainment mechanisms
Summary
Abstract: ABA triblock polyesters are synthesized using a commercially available chromium salen catalyst, in one pot, from monomer mixtures comprising epoxide, anhydride and lactone. In 2014, we reported switch catalysis using a single homogeneous dizinc catalyst which selectively polymerized mixtures of lactone (CL), epoxide (CHO), and carbon dioxide to form single-block polymer structures.[5] Experimental and theoretical studies suggested that the selectivity resulted from kinetic and thermodynamic control by the metal–chain end group.[6] This process is different from terpolymerization because two different polymerization cycles are accessed and the dominant catalytic cycle is switched by the chemistry of the catalyst–polymer chain end group.
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